This application is part of a collaborative study to explore the molecular mechanism by which HIV protease inhibitor (PI) therapy contributes to lipodystrophy and hyperlipidemia. Preliminary Results showed that ritonavir induced abnormal expression of genes responsible for fatty acid and cholesterol biosynthesis in adipose and liver of mice, suggesting that PI may interfere with the proteolytic pathway that regulates the level of activated sterol regulatory element binding protein (SREBP). Ritonavir also induced hyperlipidemia in chow-fed mice, suggesting its induction of hepatic lipoprotein biosynthesis and secretion. Four aims are designed based on these observations to test this hypothesis: HIV protease inhibitors are effective inhibitors of proteasome-mediated degradation of activated SREBP-1c and nascent apoB. The constitutive presence of activated SREBP-1c in the nucleus of adipocytes and liver, as a consequence of PI inhibition of its degradation, will result in lipodystrophy, increased lipogenesis, and insulin resistance. The inhibition of nascent apoB degradation will lead to increase hepatic lipoprotein production, thus contributing to overt hyperlipidemia. Aim 1 will use the mouse model to test the hypothesis that the adverse side-effects of ritonavir are mediated by its inhibition of proteasome degradation of activated SREBP-1c and that these effects can be suppressed by n-3 polyunsaturated fatty acid inhibition of SREBP-1 gene expression. Positive results can be extended in the companion clinical grant application to evaluate in human subjects the effectiveness of dietary n-3 fatty acid in suppressing the adverse effects of HIV protease inhibitors. Aim 2 will test the hypothesis that ritonavir also stimulates lipoprotein assembly and secretion through inhibition of proteasome-mediated apoB degradation in the liver. The potential beneficial effects of niacin, due to its proteasome-independent stimulation of apoB degradation, will also be explored. Aim 3 will determine if PI also decreases lipoprotein clearance from circulation through alteration in structure and/or activity of the lipoproteins and/or of the lipoprotein receptors. Aim 4 will compare and correlate the effectiveness of various PIs on nuclear SREBP-1c hydrolysis and lipid metabolism gene expression with their effects on hyperlipidemia, lipodystrophy, and insulin resistance. This aim ill also interact with the companion clinical grant to examine SREBP regulated gene expression in adipose and leukocytes of patients with or without hyperlipidemia. These studies will provide mechanistic information at the molecular level to explain the adverse effects of PI therapy on lipogenesis and lipoprotein metabolism. Collaboration with the companion grant will facilitate the evaluation of dietary and/or therapeutic manipulations as treatment to suppress the adverse effects of PI.